The present invention relates to a system and method for forming fused quartz glass or fused silica, more particularly, for shaping fused quartz or fused silica glass into vessels of a desired shape.
Large chambers or vessels made of fused quartz/fused silica glasses (hereinafter referred to as “fused quartz glass” for simplicity) are known in the prior art. Such vessels typically have diameters greater than 200 mm. Such vessels are desirable because they provide a controlled atmosphere for processes that require a controlled and/or non-reactive atmosphere.
Typically, these vessels are formed by welding together separate pieces of fused quartz glass. For example, a conventional forming method involves laser cutting a fused quartz glass tube in half and subsequently welding together the two half tubes and two flat plates made of fused quartz glass. The resulting vessel thus includes one or more welded seams, which may require subsequent grinding. Finally, the vessel must be fire polished to form a completed structure having the desired transparency.
However, such conventional systems and methods are labor intensive, particularly due to the large amount of welding that must be performed and the necessary subsequent grinding of the weld lines to form a completed vessel. For example, it is not uncommon for such conventional forming methods to result in over 10 feet of welding per vessel. In addition, because of the large amount of welding involved, such conventional methods can be hazardous, time-consuming and costly. Specifically, welding of quartz glass requires a high skill level and a great deal of care, as a welding error could result in the entire quartz glass piece shattering, resulting in a total loss of the costly quartz glass material. Thus, it is difficult to make fused quartz glass vessels on a large-scale commercial basis, using such conventional systems and methods.
Accordingly, it would be desirable to provide a method and system for forming quartz glass, particularly into a vessel, which requires minimal mechanical working (e.g., minimal welding and grinding). As an alternative to welding together separate quartz glass pieces, there are known in the field some forming processes by which sheet glass and other glass items are molded into a desired shape. However, such conventional molding processes are only performed for glasses having relatively low melting (Tg) temperatures (e.g., in the range of 400 to 600° C. Tg) and relatively low viscosities (e.g., in the range of 102 to 105 poise) at deformation temperatures (e.g., in the range of 400 to 1100° C.). As a result, these low melt point temperature and low viscosity glasses can be rather easily molded into a desired shape.
Fused quartz glass, on the other hand, has a relatively high melting temperature and a relatively high viscosity, and thus is much more difficult to form by conventional molding techniques. In particular, it would very difficult to attain a viscosity in the range of 102 to 105 poise for an entire large piece of fused quartz glass. Specifically, in order to attain fused quartz glass with a viscosity in this range, the quartz glass would have to be heated to temperatures of 2000° C. or more, which would result in large radiation heat losses. Further, even by heating fused quartz glass to a temperature of approximately 1600° C. (i.e., around the softening point of fused quartz glass), the glass will not have such a low viscosity (e.g., in the range of 102 to 105 poise). In particular, even at 1600° C., the viscosity of the fused quartz glass would be too high for molding or forming. Thus, forming or molding of fused quartz glass, which has a much higher melting temperature and much higher viscosities than other types of glass, is rather difficult to perform and cannot be done with conventional or off-the-shelf type furnaces used for molding of low melt point and low viscosity glasses. As such, very expensive custom furnaces and complex assemblies have been thought to be required for molding of fused quartz glass.
Accordingly, it would be beneficial to provide improved systems and methods for forming fused quartz glass, and more particularly for producing large fused quartz glass vessels. More particularly, it would be beneficial to provide simplified, efficient and cost-effective systems and methods for molding or forming fused quartz glass into a vessel or chamber free of any weld lines without the need for an expensive and custom-made furnace.